184 



CONDUCTION OF HEAT. 



2d, the planets, and satellites, and the moon ; and 3d, the fixed stars. But it 

 has been shown that the moon does not supply heat enough to affect the 

 most delicate differential thermometer, even when condensed by a burning- 

 glass. It follows, then, d fortiori, that the planets and satellites can produce 

 no sensible effect. As to the stars, it has been proved that their heating pow- 

 er must be less than that of the sun in the same proportion as their apparent 

 magnitude is less, and as no telescope has ever exhibited them with any 

 sensible magnitude, however high the power, we may safely infer that their 

 heating power is unappreciable. 



2. Electricity is a source of heat in whatever manner it may be evolved. 



3. The condensation of gases, solidification of liquids, and percussion or 

 compression of solids. 



4. Chemical combination and decomposition. 



5. The functions of animal life. 



